Possible mechanisms of chronic leprosy-related arthritis

Microbial agents induce arthritis through mechanisms such as direct infiltration of tissue and by inducing autoimmune phenomena. The mechanisms involved in this last type of arthritis have been investigated. In experimental models of adjuvant and reactive arthritis, the involvement of T cells and in some cases mycobacteria in the development of arthritis have been confirmed. Cross-reactivity boetween the 65 kD mycobacterial protein and cartilage proteoglycans has been postulated as a possible mechanism. In this study, chronic peripheral arthritis was observed in patients with Hansen's disease, in patients with resolved Hansen's and in those with paucibacillary forms. This arthritis was not related to reactional states (erythema nodosum leprosum and reversal reaction), in contrast to several reports in the literature. The mechanisms by which microbes could induce chronic arthritis are discussed herein.

Possible mechanisms of chronic leprosy-related arthritis E xperimental models have suggested that mycobacterial infections can trigger autoimmune arthritis, mainly through T-cell mediated responses.Adjuvant arthritis, experimentally induced in rats by the intradermal injection of dead mycobacteria (M.tuberculosis) suspended in mineral oil, produces chronic inflammation of the articulations in genetically predisposed animals. 1 In humans, arthritis has been reported in patients submitted to immunotherapy with BCG. 2 The role of mycobacteria in the pathogenesis of rheumatoid arthritis and other types of chronic inflammation has been suggested previously. 3In particular, mycobacterial heat-shock proteins have been considered important targets of the cellular immune response in patients with juvenile arthritis, 4 rheumatoid arthritis, 5 and of antibody production in rheumatoid arthritis patients. 6he 65 kD heat-shock protein is an important target for arthritogenic T-cell clones, mainly the aminoacid sequence 180-188. 7eripheral blood and synovial fluid T-lymphocytes from patients with rheumatoid arthritis showed increased reactivity to a mycobacterial fraction that cross-reacted with articular cartilage constituents, especially in patients with 1-10 years of disease duration. 8The response was considered specific since there was no reactivity to other mitogens or streptococcal antigens, suggesting a direct relationship between the mycobacterial antigens and the pathogenesis of rheumatoid arthritis.
Alteration in the agalactosyl immunoglobulin G (IgG) molecule was observed in patients with tuberculosis, erythema nodosum leprosum, 9 Crohn's disease, and rheumatoid arthritis. 10Agalactosyl IgG is associated with cytokine production, acute phase response and tissue injury. 10Elevation of this immunoglobulin parallels with increased binding of mycobacterial proteins to immunoglobulins. 11hronic arthritis has been described in Hansen's disease but not associated with the presence of bacilli within the joint or to reactional states. 12,13,14In a previous study by our group, 15 peripheral arthritis was observed in several patients with Hansen's disease.In the majority, the arthritis followed a chronic pattern and was not associated with leprosy reactions.Arthritis was identified in patients with negative bacilloscopy and with resolved Hansen's disease.Patients with different forms of Hansen's disease (indeterminate, dimorphous, tuberculoid and lepromatous) had arthritis.These data contrasted with studies where arthritis was related and confined to erythema nodosum reactions.
We hypothesized the possible mechanisms involved in the generation of arthritis in patients with paucibacillary Microbial agents induce arthritis through mechanisms such as direct infiltration of tissue and by inducing autoimmune phenomena.The mechanisms involved in this last type of arthritis have been investigated.In experimental models of adjuvant and reactive arthritis, the involvement of T cells and in some cases mycobacteria in the development of arthritis have been confirmed.Cross-reactivity between the 65 kD mycobacterial protein and cartilage proteoglycans has been postulated as a possible mechanism.In this study, chronic peripheral arthritis was observed in patients with Hansen's disease, in patients with resolved Hansen's and in those with paucibacillary forms.This arthritis was not related to reactional states (erythema nodosum leprosum and reversal reaction), in contrast to several reports in the literature.The mechanisms by which microbes could induce chronic arthritis are discussed herein.UNITERMS: Mycobacteria, cellular immunity, humoral immunity, leprosy arthritis.
forms, with resolved Hansen's disease and without reaction.In addition, the long duration of the articular manifestation suggested that somehow it has been perpetuated.
Pathogenic mechanisms similar to those of adjuvant arthritis may be involved in the chronic articular phenomena in Hansen's disease, particularly if the homology between M. leprae and M. tuberculosis is considered.In adjuvant arthritis, the cellular immune response to mycobacterial antigens has been detected, and is probably involved in the development of arthritis. 16The identification of the 65 kDa protein as the main target of T-cell mediated responses, 17,18 its cross-reactivity to purified cartilage proteoglycans, 19 including in rheumatoid arthritis, 20 has emphasized its importance in arthritis during mycobacterial infections, and possibly in chronic leprosyrelated arthritis.The 65 kDa protein is an immunodominant target for T-cell responses in Hansen's disease, and shares homology with the human 60 kDa protein. 21The response to bacterial antigens stimulates T-cell clones that may cross react with intrinsic components of the joints in susceptible individuals.
The auto-antibodies generated in Hansen's disease are considered natural antibodies with low affinity, and therefore their possible participation in the pathogenic mechanisms of chronic leprosy-related arthritis is improbable.In our study, no correlation was found between auto-antibodies and arthritis.
Although the humoral response was not considered an important mechanism for defense or for the clinical manifestations of Hansen's disease, it may indicate that B cells had been activated as part of the network of immune alterations occurring during mycobacteria recognition.In Hansen's disease, auto-antibodies are low-affinity antibodies and may only be important when forming immunocomplexes.Tubercle bacilli have been considered potent adjuvants for induction of polyclonal B lymphocytes activation. 22In addition, no cross-reaction was observed between the 70 kDa mycobacterial protein and human structures. 23The polyclonal B-cell activation in lepromatous leprosy is probably a consequence of cytokine production by T lymphocytes.
Perpetuation of arthritis may be due to the persistence of antigens inside the joints or to the homing of the continually activated T lymphocytes, 24 as demonstrated in adjuvant arthritis and inflammatory arthritis.In particular, it has been shown that when 65 kDa specific-T lymphocytes migrate to the joint, articular lymphocytes are responsible for the continuation of the immune response, mainly because these cells are memory cells. 17,24astocytes may also be able to amplify the response within the joint in chronic arthritis. 25In reactive arthritis, an augmented T-cell response was detected in synovialderived cells when compared to peripheral blood cells responses, demonstrating a local activation of T cells, 18 or migration of chronically activated cells.
Several patients with Hansen's disease and chronic arthritis required specific treatment for the articular manifestations, such as chloroquine or sulfasalazine. 15herapeutic results were very good and in many patients, symptoms disappeared even after drug use had been interrupted.Inhibition of the antigen presentation by chloroquine may be one of the possible mechanisms by which this drug ameliorates M. leprae-induced arthritis.
The presence of arthritis in all types of Hansen's disease and in patients without reactions emphasizes that the contact with the bacilli may trigger chronic immunological responses in genetically predisposed individuals.Indeed, chronic synovitis was demonstrated in biopsies of patients with active Hansen's disease and during reaction, indicating that chronic inflammation may occur parallel to acute manifestations. 26POWELL and SWAN 27 also detected chronic inflammatory infiltrates and fibromatous reaction in bone tissue of Hansen's disease patients.
ROOK clarified the immunological pathways by which slow-growing bacteria may induce and perpetuate chronic arthritis, such as mycobacterial infections. 28In brief, invading bacteria activate T lymphocytes which release lymphokines chronically.Those lymphokines activate B lymphocytes to produce agalactosyl immunoglobulins.In addition, bacterial antigens stimulate autoreactive clones that may induce immune responses mediated by antibodies or by T-cells.It is believed that local immune responses also occur in addition to the homing of sensitized T lymphocytes to the joint.
Studies of the mechanisms involved in arthritic manifestation in infectious diseases may clarify the possible pathways by which chronic inflammatory diseases are induced, and suggest new therapeutical options, such as peptide-based immunotherapy. 29